Differences between planning and scheduling, finite and infinite

Finite Scheduling

Scheduling type within capacity planning that takes account of the capacity loads which already exist.  Finite scheduling calculates the start and finish dates for operations in the order.  It is a detailed scheduling strategy with which you schedule orders and operations, taking into account the existing resource load. A resource overload cannot occur.

Infinite Scheduling 

A detailed scheduling strategy with which you schedule orders and operations, without taking into account the existing resource load. It is therefore possible for resource overloads to occur. 

R/3 does planning without consideration for capacity situations. So if MRP says you need 500 parts on 3/1/04, it schedules them all to be built at the same time, even though you can only do 100 at a time. Assume you have a fixed lot size of 100, you'll get 5 planned orders for 100 to start on the same day. This is "Infinite Planning". APO would recognize that constraint, and instead schedule out the 5 orders over time. The important part of that is that it also will schedule out the deliveries of the components for 5 different days. This is "Finite Planning". 

Now, assume old fashion MRP. It schedules all 5 orders for the same day, and the buyers go out an get all of the components for the same day. Then the planner realizes he can't do all 5, and manually changes the schedule, and manually spreads out the 5 orders. The buyers will recieve rescheduling notifications, but not until the scheduler does the manual rescheduling.
You could call this "Infinite Scheduling", but that only means the same thing as Infinite Planning. 

But, SAP has "Capacity Leveling". What that means is you run another program after MRP (CM27 and CM28), which can be run in batch mode overnight. (There is a ton of configuration and thinking that will be required to do this!). The capacity leveling program will recognize the constrant at the work center level, and fill up the first day, then re-schedule the next
order to the next available capacity, then the next order searches for available capacity, and so on. This is called "Finite Scheduling". The problem with this is the opposite of Infinite Planning, which is it doesn't take Material availablity into consideration! The system will re-schedule a production order without thinking about whether the materials will be available or not. 

Finite Planning does Finite Scheduling at the same time. If there is no capacity available on the desired date, the system looks for when capacity IS available. Then it stops to see if Materials will also be available (usually based on the lead-time for those components). If there is a material problem, then the system figures out when the materials WILL be available, and then 
checks to see if capacity is available on THAT day, and if so, it blocks off capacity, and allocates the materials for that day. 

SAP PP Tips by :  Nagesh

See also
Explain Detached Order Assembly

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